Borderline personality disorder (BPD) is a commonly occurring, severe, and costly condition for which treatment efforts have been hindered by several factors. First, extant treatments for BPD are long-term, intensive and consist of multiple components, largely focused on resolving the life-threatening dysregulation that characterizes this disorder. It is important to note, however, that most individuals diagnosed with BPD never attempt suicide or require inpatient hospitalization. Multi-component interventions may not be the most efficient approach for patients with less severe levels of BPD and also make it difficult to draw conclusions regarding which treatment strategies are influencing mechanisms maintaining symptoms. Additionally, extant BPD treatments do no explicitly address high rates of comorbidity with anxiety and depressive disorders; high levels of co-occurrence amongst these disorders underscores the utility of identifying transdiagnostic treatment components relevant to maintaining mechanisms across diagnostic boundaries. The proposed Mentored Patient-Oriented Research Career Development Award (K23) is a four-year plan in support of the applicant's long-term career goal to become a clinical scientist proficient in developing parsimonious, easily disseminated treatments for BPD and other emotional disorders. The immediate goal of the K23 award is for the applicant to become skilled at a number of methodological approaches aimed at isolating the effects of disorder and treatment mechanisms. The applicant's training and development thus far has supported these long-term goals. Throughout her graduate work, she conducted studies aimed at identifying factors that maintain emotional disorder symptoms and used this information to conduct several small-scale investigations of treatment strategies targeting such factors. The specific goal of the proposed research study is to isolate the unique effect of acting inconsistent to emotion-driven action tendencies, a treatment component included in leading treatments for BPD, anxiety and depressive disorders. This project will be completed in two phases. The goal of Phase I, in line with an experimental therapeutics approach, is to investigate the effect of acting inconsistent with emotion-driven behavioral urges on emotional intensity in a sample of individuals diagnosted with BPD in the context of a single-case experiment (alternating treatment design). Phase II will also utilize single-case experimental design (in this case a multiple baseline study) to explore the effects of brief intervention focused solely on acting inconsistent to emotional action tendencies on emotional intensity, tolerance of emotions, and BPD symptoms in a sample diagnosed with BPD. The training plan closely matches the proposed research and long-term goals with an emphasis on training activities that will facilitate the candidate's development as an independent investigator. Specifically, the training aims are to: (1) Develop advanced understanding of research methodology aimed at investigating putative mechanisms of action in behavioral treatments (e.g., single-case experimental design, statistical methods); (2) Gain experience in research methodology specific to a BPD population (e.g. diagnostic and clinical change assessment, recruitment and retention strategies); (3) Enhance training in multi-modal assessment of clinical targets and outcomes (e.g., behavioral assessment). Boston University's Center for Anxiety and Related Disorders, where all research and the bulk of the training activities will take place, is a world-renown clinical research institution with a successful history of treatment development research. Overall, the broader aim of these research and training goals is to address the need for improved treatments for BPD. This study will answer important theoretical questions about the mechanism of treatment change, and might lead to more efficacious, cost-effective, and easily disseminable treatment strategies for BPD, a severe and understudied disorder.